A method for tracking the location of mobile units, comprises providing a plurality of mobile units each having a wireless transmitter and a unique address and at least one stationary base unit having a phase array antenna with antenna elements. A signal including an address is received from at least one mobile unit by the at least base unit via the phase array antenna. The phase difference of the signal arriving at the antenna elements from each mobile unit is measured and the coordinates of the location of each mobile unit are calculated as a function of the phase differences.